(A) model of distributed control for resource management and its applications

Abstract

In a distributed computer system, where a set of autonomous hosts are geographically dispersed and integrated by a distributed operating system or distributed database system, processes often engage into cooperative or competing efforts to exploit the potential benefits of distributed computer system. An abstract entity usually has the responsibility of the coordination of process. The abstract entity is called a distributed control system, when it consists of two or more controllers, and when each controller has different and only limited view of the global state. Due to the limited view of global state, distributed control system should provide a means to all controllers, which enables these controllers to obtain a consistent and identical view of the global state of the system without a unique centralized database structure. However, since the message passing (i.e., no global memory) is the only means of communications and since the message propagation time is finite and unpredictable, the complete and consistent state information of the entire system may not be available to any controller. As a result, in distributed environment, controllers have to decide their actions based on the partially correct and outdated information, but the actions do not violate the consistency of the global state. Moreover, communication overheads occur considerably, which is caused by the exchange of the state information and coordination of the activities. Thus, it is important to make the distributed control system impose extra traffic to the communication channels as little as possible. In this thesis, a model of distributed control for resource management systems with less communication overhead is proposed. One of the main idea is to replicate the state information to several sites, and relax the copy consistency constraint resulting from the replication. The other is to make each process deduce the global state from known state information to itself, which may be outdated...